The present invention relates to a circuit arrangement for the current limiting interruption of high voltage direct and alternating currents. More particularly the present invention relates to such a circuit arrangement including at least one commutating switch which is connected to a residual current switch, and at least one shunt path connected in parallel with the commutation switch with the shunt path including a temperature dependent resistor with a highly positive temperature coefficient.
Circuit arrangements for the current limiting interruption of direct and alternating currents at high voltage are known in which one or a plurality of commutation switches are connected in parallel with capacitances and resistances for the intermediate commutation and generation of a zero current passage in the commutation switch. In these known circuit arrangements the capacitances are usually provided with series-connected spark paths so that they become effective only after a certain firing voltage has been reached by the commutation switch. After the intermediate commutation the current to be switched off is then handled by a highly resistive energy absorber. Thus the current is reduced to a residual value which can be switched off by a series-connected residual current switch. Such a circuit arrangement is disclosed in the publication ETZ-A volume 91 (1970), pages 79-82.
In these arrangements, the expenditures for the shunt path are considerable if commercially available elements such as capacitors and silicon carbide resistors, for example, are used. A further drawback of silicon carbide absorbers is that this material has a thermal cooling time constant of several 10 minutes and thus can be subjected to renewed loads only after switch-off for a relatively long period of time. Alternatively, the volume of the absorber must be substantially increased.
Circuits are also known in which one or a plurality of series-connected power switches are connected in parallel with temperature dependent resistors having a high positive temperature coefficient. These parallel resistors bridge the interruption arc and are provided to facilitate quenching by attenuating the recurring voltage. The parallel resistors are low-ohmic when cold and thus facilitate commutation. Upon completion of the commutation, the resistors are heated by the switch-off current and thus increase their resistance value by a multiple. The residual current is again switched off by a series-connected residual current switch. Such a circuit arrangement is shown in German Pat. No. 969,067. It has been found, however, that a direct parallel connection of a commutation switch and a temperature dependent resistor is not favorable for commutation.